69 
and the Carboniferous limestone atsome points attains a thick- 
ness of 1,200 or 1,500 feet, full of crinoids, etc. In some 
places this limestone has all the aspect of a great shore-reef, 
its edges almost vertical cliffs, hundreds of feet high, and full 
of caverns and wave-lines worn by the ancient sea. 
Beneath the limestone is a brown or yellow sandstone, 
600 or 700 feet thick, non-fossiliferous, and of undetermined 
age. 
” Passing westward to the Hueco mountains, a like section is 
again found, the dip also being eastward. Here the Carbon- 
iferous forms the crest, and is underlaid by Lower Silurian, 
which ia turn rests upon gneiss. 
The most interesting and important series, however, was 
found thirty miles farther west, in the Organ mountains, close 
to the city of El Paso. Here the base is a coarse feldspathic 
granite, very similar to much of the eastern gneiss, and upon 
it rests: 
I. Quartzite, passing upward mto , 
II. Sandstone (Potsdam), filled with Scolithus linearvs. 
III. Crystalline limestone (Calciferous), containing several 
species of fossils resembling Archeocyathus, and rarely a 
gasteropod, like Pleurotomarta. 
IV. Magnesian limestone, (Chazy), with flints, and contain- 
ing some straight cephalopods and a feceplaculttes. 
V. Black limestone (Trenton), with Maclurea abundant, 
Orthis, Ortheceras, and a “ chain coral.” 
VI. Lower Hudson, very rich in corals. 
VIL Upper Hudson, with Orthis, ete., and many charac- 
teristic fossils of the period. 
The dip of all these beds is about 30° west, facing the 
eastward dipping rocks of the Hueco range. Their total 
thickness exceeds 1,200 feet. 
Upon them rests a great limestone reef, some 400 feet 
thick, unconformable, dipping west about 10°, and passing 
upward into what appears to be Carboniferous, judging from 
the position of rocks of that age on the ranges lying to the 
north and east. Its lower portion, however, contains some 
imperfect fossils resembling Pentamerus, and suggesting an 
Upper Silurian age; while at the base is a conglomerate, 
made up of pebbles of beds V, VI, and VIY, which seems to 
hold the position of the Oneida. 
No Devonian can be recognized at any point. 
‘Tur PRESIDENT remarked that this account has peculiar 
interest. Among many important points, it shows the great 
